This experiment was conducted to determine the effects of Marigold Oil Extract (MOE) on blood parameters, immune system and livers of broiler chickens in a 42-day period. A total of 200 Ross 308 broiler chickens were allocated to five dietary treatments with four replicates of 10 birds each. The experimental treatments included a negative control group (basal diet without using any MOE and carbon tetrachloride, CCl4), a positive control group}CCl4(1 mg/kg BW) and basal diet without using any MOE {and three levels of MOE at 150, 300 and 450 mg/kg BW together with CCl4 and basal diet. Levels of blood parameters (SGOTو SGPT) increased, and MOE was able to reduce the negative effects of this toxic substance. When the broilers were 33 and 42 days old, the liver weights in treatments receiving various concentrations of MOE besides CCl4 were significantly lower than those in the treatment receiving CCl4. As for the indices related to immune system, the IgG level in the treatment receiving 300 mg/Kg of MOE in addition to CCl4 was significantly highercompard to the negative control and level of 150 mg/Kg of MOE . Examination of histopathological changes in the liver tissues revealed that the positive control group suffered the maximum tissue damage in the central vein, hepatocytes, sinusoids, and the triad port (the hepatic artery, the portal vein, and the bile ducts), while the negative control group exhibited the minimum tissue damage. However, treatments receiving MOE together with CCl4 showed greater recovery in the tissues compared to the positive control group. In conclusion,These results indicated the protective effects of MOE on the liver. These effects are probably due to the ability of the flavonoids found in this plant to suppress the bioactivation of CCl4 and, hence, to suppress the activity of Cyt P450, and due to the neutralization of free radicals by the flavonoids.